Every now and then, maybe every 10 to 20 minutes, winbind ceases to properly resolve NSS names. This became a problem for me in Intrepid, though I did see the problem in Hardy very infrequently. It is now a regular occurance.
I have no name!@station-1:~$ whoami
whoami: cannot find name for user ID 1786588783
Obviously this causes many apps to cease functioning. If I run wbinfo -u, it begins working again:
I have no name!@station-1:~$ whoami
ISI\jhaltom
It looks like running wbinfo -u pokes winbind in some fashion that causes it to answer requests again.
My view of this is that winbind SHOULD have a local cache of uid to sid/name. It should *never* empty a record from this cache unless superceeded by another valid answer from the domain. There's no good reason for it to do so.
I've got debugging on. When running a failing 'whoami', I see the following:
[2008/10/24 11:31:25, 3] winbindd/winbindd_user.c:winbindd_getpwuid(466)
[30914]: getpwuid 1786588783
[2008/10/24 11:31:31, 5] winbindd/winbindd_dual.c:async_reply_recv(264)
Could not receive async reply from child pid 30906
[2008/10/24 11:31:31, 5] winbindd/winbindd_async.c:query_user_recv(1089)
Could not trigger query_user
[2008/10/24 11:31:31, 5] winbindd/winbindd_user.c:getpwsid_queryuser_recv(235)
Could not query domain ISI SID S-1-5-21-1957994488-1482476501-725345543-1207
[2008/10/24 11:31:31, 5] winbindd/winbindd_dual.c:winbind_child_died(476)
Already reaped child 30906 died
So, it fails to query the domain. For some reason this causes it to not answer with a cached response. I don't know why!
wbinfo -u runs as expected. It says the domain has users. The second run of whoami, after wbinfo -u, looks like this:
[2008/10/24 11:32:02, 6] winbindd/winbindd.c:new_connection(716)
accepted socket 19
[2008/10/24 11:32:02, 3] winbindd/winbindd_misc.c:winbindd_interface_version(757)
[30932]: request interface version
[2008/10/24 11:32:02, 3] winbindd/winbindd_misc.c:winbindd_priv_pipe_dir(790)
[30932]: request location of privileged pipe
[2008/10/24 11:32:02, 3] winbindd/winbindd_user.c:winbindd_getpwuid(466)
[30932]: getpwuid 1786588783
[2008/10/24 11:32:02, 7] winbindd/winbindd_idmap.c:winbindd_sid2gid_async(363)
winbindd_sid2gid_async: Resolving S-1-5-21-1957994488-1482476501-725345543-513 to a gid
So, this sucks. Basically makes my desktop unusable. Every few minutes apps begin breaking. I've got wbinfo -u running on a loop in the background to keep it working.

Sorry for my tardyness.
It does seem to be fixed in whatever version is in Jaunty. For a minute I thought it was still there, but I think there's some new interaction with network manager. If winbind starts before Network Manager brings the interface up, Winbind doesn't work. I'll find/open a new bug for that issue however.